1 H-NMR and GC for detection of adulteration in commercial essential oils of Cymbopogon ssp.

INTRODUCTION: Essential oils of Cymbopogon nardus and C. winterianus have fungicidal, bactericidal, and insect repellent activities. In addition, they are components of fragrances, cosmetics, and household products. The growing demand for essential oils has intensified adulteration practices of such products. OBJECTIVES: To evaluate the authenticity and quality of citronella commercial essential oils based on chemical composition [by gas chromatography mass spectrometry (GC-MS)] and the contents of its major constituents [by 1 H-NMR, and gas chromatography with a flame ionisation detector using internal standardisation (GC-IS)]. MATERIALS AND METHODS: The chemical composition of essential oil was determined by GC-MS. Major components were quantified by 1 H-NMR and the results compared to those obtained by GC-IS. RESULTS: The adulteration of oils was verified by GC and 1 H-NMR. In the pure oils, the results obtained by 1 H-NMR were similar to those obtained by GC-IS for most of the oils. However, in adulterated oils, signal overlap prevented the quantification of citronellol and geraniol by NMR. Importantly, due to dilution with dipropylene glycol it was not possible to quantify citronellal using 1 H-NMR. However, for both pure and adulterated oils, GC-IS method proved successful in quantifying notable constituents. CONCLUSION: All the methods used proved efficient in detecting adulteration. However, whilst GC-IS provided quantification of constituents of interest, both in pure and adulterated oils, their quantification by NMR was only possible in non-adulterated samples. None of the oils evaluated presented a composition within the threshold established by British Pharmacopoeia quality standards.

Tailoring Natural Abenquines To Inhibit the Photosynthetic Electron Transport through Interaction with the D1 Protein in Photosystem II.

Abenquines are natural N-acetylaminobenzoquinones bearing amino acid residues, which act as weak inhibitors of the photosynthetic electron transport chain. Aiming to exploit the abenquine scaffold as a model for the synthesis of new herbicides targeting photosynthesis, 14 new analogues were prepared by replacing the amino acid residue with benzylamines and the acetyl with different acyl groups. The synthesis was accomplished in three steps with a 68-95% overall yield from readily available 2,5-dimethoxyaniline, acyl chlorides, and benzyl amines. Key steps include (i) acylation of the aniline, (ii) oxidation, and (iii) oxidative addition of the benzylamino moiety. The compounds were assayed for their activity as Hill inhibitors, under basal, uncoupled, or phosphorylating conditions, or excluding photosystem I. Four analogues showed high effectiveness (IC50 = 0.1-0.4 µM), comparable with the commercial herbicide diuron (IC50 = 0.3 µM). The data suggest that this class of compounds interfere at the reducing side of photosystem II, having protein D1 as the most probable target. Molecular docking studies with the plastoquinone binding site of Spinacia oleracea further strengthened this proposal.

Tetraoxanes as a new class of efficient herbicides comparable with commercial products.

BACKGROUND: Several 1,2,4,5-tetraoxanes were synthesised, and their herbicidal activity was tested against weeds and compared with the activity of commercial herbicides glyphosate and imazethapyr. RESULTS: The compounds were prepared by reacting carbonyl compounds with hydrogen peroxide under acid catalysis, affording 1,1-dihydroperoxides (36-91%) that were further converted into 1,2,4,5-tetraoxanes (10-52%) under similar reaction conditions. All products were evaluated against Sorghum bicolor and Cucumis sativus at 0.0125-1.0 mM, and several tetraoxanes caused >70% inhibition of the growth of roots and aerial parts. The most active products were evaluated against the weeds Sorghum arundinaceum, Euphorbia heterophylla, Brachiaria brizantha and Bidens pilosa. Some compounds were highly effective (>80% inhibition at 1.0 mM) against the weeds, showing activity comparable with that of glyphosate or imazethapyr. One of the tetraoxanes was selective, being inactive against dicotyledonous species while inhibiting the roots and aerial parts of monocotyledonous species by 92.9-97.5%, which is comparable with the effect of glyphosate. CONCLUSIONS: Tetraoxanes constitute a new class of effective herbicides with great potential for commercial development.

Cyclopent-4-ene-1,3-diones: a new class of herbicides acting as potent photosynthesis inhibitors.

In a recent paper, we reported the synthesis and photosynthesis-inhibitory activity of a series of analogues of rubrolides. From quantitative structure-activity relationship (QSAR) studies, we found that the most efficient compounds are those having higher ability to accept electrons. On the basis of those findings, we directed our effort to synthesize new analogues bearing a strong electron-withdrawing group (nitro) in the benzylidene ring and evaluate their effects on photosynthesis. However, the employed synthetic approach led to novel cyclopent-4-ene-1,3-diones as major products. Here, we report the synthesis and mechanism of action of such cyclopent-4-ene-1,3-diones as a new class of photosynthesis inhibitors. These compounds block the electron transport at the QB level by interacting at the D1 protein at the reducing side of Photosystem II and act as Hill reaction inhibitors, with higher activity than the corresponding rubrolides. To the best of our knowledge, this is the first report on the photosynthesis inhibitory activity of cyclopentenediones.

Inhibition of Enterococcus faecalis biofilm formation by highly active lactones and lactams analogues of rubrolides.

Seven ß-aryl substituted γ-alkylidene-γ-lactones analogues of rubrolides were synthesized from mucobromic acid and converted through a lactamization with isobutylamine into their corresponding γ-hydroxy-γ-lactams (76-85%). These lactams were converted into (Z)- and (E)-γ-alkylidene-γ-lactams (23-45%). All compounds were fully characterized by IR, NMR ((1)H and (13)C), COSY and HETCOR bidimensional experiments, and NOE difference spectroscopy experiments when necessary. Evaluation of these three different classes of compounds against Enterococcus faecalis biofilm formation showed that all classes are active and the highest biofilm inhibition activity was caused by lactam 13f (IC50 = 0.76 µg/mL). Moreover, in almost all cases at least one of the lactams is more active than its correspondent γ-alkylidene-γ-lactone. The use of rubrolides as a lead structure has proven successful for the identification of new compounds displaying novel antibacterial activities, namely biofilm inhibition, which have the potential for the development of antimicrobial drugs targeted to inhibition of the initial stages of bacterial infections, rather than bacterial viability. Such drugs are less prompt to induce bacterial resistance, being therefore a more cost-effective investment for pharmaceutical research.

γ-Alkylidene-γ-lactones and isobutylpyrrol-2(5H)-ones analogues to rubrolides as inhibitors of biofilm formation by gram-positive and gram-negative bacteria.

Several molecules have been discovered that interfere with formation of bacterial biofilms, opening a new strategy for the development of more efficient treatments in case of antibiotic resistant bacteria. Amongst the most active compounds are some natural brominated furanones from marine algae Delisea pulchra that have proven to be able to control pathogenic biofilms. We have recently reported that some rubrolide analogues are able to inhibit biofilm formation of Enterococcus faecalis. In the present Letter we describe results of the biological evaluation of a small library of 28 compounds including brominated furanones and the corresponding lactams against biofilm formation of Staphylococcus aureus, Pseudomonas aeruginosa, Staphylococcus epidermidis and Streptococcus mutans. Our results showed that in general these compounds were more active against biofilms of S. epidermidis and P. aeruginosa, with little or no inhibition of planktonic bacterial growth. In some cases they were able to prevent biofilm formation of P. aeruginosa at concentrations as low as 0.6 µg/mL (1.3 µM, compound 3d) and 0.7 µg/mL (1.3 µM, 3f). Results also indicate that, in general, lactams are more active against biofilms than their precursors, thus designating this class of molecules as good candidates for the development of a new generation of antimicrobial drugs targeted to biofilm inhibition.

Synthesis of rubrolide analogues as new inhibitors of the photosynthetic electron transport chain.

Many natural products have been used as a model for the development of new drugs and agrochemicals. Following this strategy 11 rubrolide analogues, bearing electron-withdrawing and -donating groups at both benzene rings, were prepared starting from commercially available mucobromic acid. The ability of all compounds to inhibit the photosynthetic electron transport chain in the chloroplast was investigated. The rubrolide analogues were effective in interfering with the light-driven ferricyanide reduction by isolated chloroplasts. The IC(50) values of the most active derivatives are in fact only 1 order of magnitude higher than those of commercial herbicides sharing the same mode of action, such as Diuron (0.27 µM). QSAR studies indicate that the most efficient compounds are those having higher ability to accept electrons, either by a reduction process or by an electrophilic reaction mechanism. The results obtained suggest that the rubrolide analogues represent promising candidates for the development of new active principles targeting photosynthesis to be used as herbicides.

Synthesis of novel α-santonin derivatives as potential cytotoxic agents.

Ten novel α-santonin derivatives have been synthesized as cytotoxic agents. The in vitro antitumor activity of these compounds has been evaluated against cancer cells lines. Structure-activity relationships indicate that α-methylene-γ-lactone and endoperoxide functionalities play important roles in conferring cytotoxicity. The compounds 2-4, possessing the α-methylene-γ-lactone group showed IC50 values between 5.70 and 16.40 µM. Mixture of isomers 5 and 6, with the α-methylene-γ-lactone and endoperoxide functionalities, displayed the greatest activity, with IC50 values between 1.45 and 4.35 µM. The biological assays conducted with normal cells revealed that the compounds 2, 5 and 6 are selective against cancer cells lines tested. Bioactive lactones described herein and in our previous report did not cause disruption of the cell membrane in mouse erythrocytes.

Synthesis and biological evaluation of new ozonides with improved plant growth regulatory activity.

The iron oxyallyl carbocation generated from 2,7-dibromocycloheptanone was induced to undergo [4 + 3] cycloaddition reactions with various furans, affording a series of 12-oxatricyclo-[4.4.1.1(2,5)]-dodec-3-en-11-one adducts. Similar methodology was used to prepare two additional cycloadducts using menthofuran and two homologous aliphatic dibromoketones. Dipolar cycloaddition of ozone to the adducts afforded the corresponding secondary ozonides (i.e., 1,2,4-trioxolanes) in variable yields. Ozonides were investigated by quantum mechanics at the B3LYP/6-31+G* level to study structural features including close contacts which may be responsible for enhancing ozonide stability. The effect of these ozonides and their corresponding precursor cycloadducts upon radicle growth of both Sorghum bicolor and Cucumis sativus was evaluated at 5.0 x 10(-4) mol L(-1). The most active cycloadducts and ozonides were also evaluated against the weed species Ipomoea grandifolia and Brachiaria decumbens, and the results are discussed. Compared to ozonides previously synthesized in our laboratory, the new ozonides described herein present improved plant growth regulatory activity.

Synthesis and phytotoxic activity of ozonides.

The [4 + 3] cycloaddition of the proper furans with the oxyallyl cation, generated in situ from 2,4-dibromopentan-3-one, produced a series of 8-oxabicyclo [3.2.1]oct-6-en-3-ones. Exposure of the oxabicycles to ozone afforded the corresponding 8,9,10,11-tetraoxatricyclo[5.2.1.1 (2,6)]undecan-4-ones in variable yields (7-100%). The phytotoxic properties of these ozonides (or 1,2,4-trioxolanes) and their oxabicycle precursors were evaluated as the ability to interfere with the growth of Sorghum bicolor and Cucumis sativus seedlings. Among oxabicycles, the highest inhibitory activity was shown by compounds possessing a alpha,beta-unsaturated carbonyl moiety. A differential sensitivity of the two crops was evident with ozonides. The most active compounds were also tested against the weed species Ipomoea grandifolia and Brachiaria decumbens. To the best of our knowledge, this is the first article describing ozonides as potential herbicides.

Effect of storage time on the composition and content of wood extractives in Eucalyptus cultivated in Brazil.

Lipophilic wood extractives commonly referred to as pitch, cause significant problems for the pulp and paper industries. The reduction of these extractives is an important aspect that concerns industries around the world. In the present work the change in the amount and chemical composition of lipophilic extractives from Eucalyptus spp. stored for 20, 40, 60, 100, 140 and 180 days after harvesting was investigated. The results showed a decrease in extractives content with storage time, with the most significant decrease occurring 60 days after harvesting. In addition, fatty acids and sterols were the main classes of compounds responsible for the significant decrease in extractive content. Data were analyzed by principal component analysis. PC1 explains approximately 99% of the total variance, and beta-sitosterol was the major compound responsible for the differentiation. These studies demonstrate that in terms of economical aspects, quality of the pulp and paper and minimization of pitch formation, the best period of wood storage is 60 days.

Synthesis of 3-(4-Bromobenzyl)-5-(aryl methylene)-5H-furan-2-ones and their activity as inhibitors of the photosynthetic electron transport chain.

A series of 12 3-(4-bromobenzyl)-5-(arylmethylene)-5 H-furan-2-one lactones, designed using the naturally occurring toxin nostoclides as a lead structure, were synthesized and screened as potential inhibitors of photosynthetic electron transport. The structures were confirmed by (1)H and (13)C NMR, MS, and IR analyses. Their biological activity was evaluated both in vitro, as the ability to interfere with light-driven reduction of ferricyanide by isolated spinach chloroplasts, and in vivo, as the capability to inhibite the oxygen production by intact Chlorella cells. Some of the compounds exhibited inhibitory properties in the micromolar range against basal and phosphorylating electron flow from water to K 3[Fe(CN) 6], with no effect on uncoupled electron flow. Thus, they seem to behave as energy-transfer inhibitors. Although poor solubility in water may limit their effectiveness, the active derivatives could present structures to be exploited for the design of new substances endowed with herbicidal activity.

Toxicidade de amidas análogas à piperina a larvas de Ascia monuste orseis Godart (Lepidoptera: Pieridae) e Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) / Toxicity of piperine amide analogs to larvae of Ascia monuste orseis Godart (Lepidoptera: Pieridae) and Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

Foi avaliada, no presente estudo, a toxicidade de amidas análogas à piperina utilizando-se larvas de 3° instar de Ascia monuste orseis Godart e Spodoptera frugiperda (J.E. Smith). Os bioensaios consistiram na aplicação tópica de 0.5 æl das seguintes amidas: N-isopentil-(3,4-metilenodioxifenil)-amida, N-isopropil-(3,4-metilenodioxifenil)-amida, N-hexil-3-(3,4-metilenodioxifenil)-amida e butóxido de piperonila. Os valores de DL50 (mg i.a./ mg larva) das amidas N-isopropil e N-hexil para A. monuste foram 0.278 e 0.004, respectivamente; para S. frugiperda foram: 1.359 e 0.613, respectivamente. O maior valor das inclinações das curvas de dose-resposta dentre os compostos, para ambas as espécies de inseto foi obtido para N-isopropil, o que indica maior homogeneidade de resposta a esse produto. N-isopropil foi o composto que se mostrou mais promissor como inseticida pois foi mais tóxico a ambas espécies-praga investigadas.

The objective of this study was to evaluate the toxicity piperine amide analogs to 3rd-instar larvae of Ascia monuste orseis Godart and Spodoptera frugiperda (J.E. Smith). The bioassays were based on the topical application of 0.5 æl of the following amides: N-isopenthyl-(3,4-metilenodioxiphenyl)-amide, N-isopropyl-(3,4-metilenodioxiphenyl)-amide, N-hexyl-3-(3,4-etilenodioxiphenyl)-amide and piperonyl butoxide. The DL50 (mg a.i./ mg larva) values of the amides N-isopropyl e N-hexyl to A. monuste orseis were 0,278 and 0,004, respectively, and to S. frugiperda were 1.359 and 0.613, respectively. The steeper slopes of the dose-response curves for both species were obtained with N-isopropyl, indicating the higher homogeneity of response of the pest species studied to this compound. N-isopropyl was also the most promising piperine synthetic analog as insecticide agent among the compounds studied because it was the most toxic amide to both insect-pest species.